Remote systems, such as vehicles, have been introduced that include locomotion power derived from electricity received from an energy storage device such as a battery. For example, hybrid electric vehicles include on-board chargers that use power from vehicle braking and traditional motors to charge the vehicles. Vehicles that are solely electric generally receive the electricity for charging the batteries from other sources. Battery electric vehicles (electric vehicles) are often proposed to be charged through some type of wired alternating current (AC) such as household or commercial AC supply sources. The wired charging connections require cables or other similar connectors that are physically connected to a power supply. Cables and similar connectors may sometimes be inconvenient or cumbersome and have other drawbacks. Wireless charging systems that are capable of transferring power in free space (e.g., via a wireless field) to be used to charge electric vehicles may overcome some of the deficiencies of wired charging solutions. As such, wireless charging systems and methods that efficiently and safely transfer power for charging electric vehicles are desirable.
In a multi-strand circular or rectangular coil, for example, a coil used for a base pad of wireless power transfer systems, inductance of strands, including both self-inductance of each strand and mutual inductance between strands, can be slightly different due to their positions in a winding structure. This inductance variation may cause a large current variation between stands in a multi-strand coil due to high mutual inductance between them. In a special case, self-inductance may be equal but mutual inductance between pairs of strands are unequal and causing current variation. A current variation can cause reductions in coupling and/or increased losses and thus reduced power transfer efficiency. To reduce the current variation, inductance of strands needs to be equalized and/or compensated.